Stabilization process for thermally developable light-sensitive elements

ABSTRACT

A stabilized, thermally developed, light-sensitive element having been stabilized after development with a solution containing at least one organic compound of the group represented by the general formulas:

United States Patent 2,432,506 12/1947 Chiltonetal.

Inventors Appl. N 0. Filed Patented Assignee Priority Kinji Ohkubo; 1 Takao Masuda, both of Kanagawa, Japan 688,695

Dec. 7, 1967 Nov. 2, 197 1 Fuji Shashin Film Kabushiki Kaisha Kanagawa, Japan Dec. 10, 1966 Japan STABILIZATION PROCESS FOR THERMALLY DEVELOPABLE LIGHT-SENSITIVE ELEMENTS 1 Claim, No Drawings U.S. Cl 96/95, 96/61, 96/67,96/114.1 Int. Cl G03c l/06 Field of Search 96/61, 67, 95. 1 14.1

References Cited UNITED STATES PATENTS Primary Examiner-William D. Martin Assistant Examiner-M. Sofocleous Attorney-Sughrue, Rothwell, Mion, Zinn and Macpeak ABSTRACT: A stabilized, thermally developed, light-sensitive element having been stabilized after development with a solution containing at least one organic compound of the group represented by the general formulas:

STABILIZATION PROCESS FOR THERMALLY DEVELOPABLE LIGHT-SENSITIVE ELEMENTS BACKGROUND OF THE INVENTION 1. Field of the Invention the present invention relates to a process for stabilizing a photographic light-sensitive element which can be developed by heating.

2. Description of the Prior Art In general, as a photographic light-sensitive element, there has been most widely used a photographic light-sensitive element in which a silver halide is employed, since such a photographic silver halide light-sensitive element has excellent sensitivity and gradation as compared with electrophotographic light-sensitive elements'and other photographic light-sensitive elements employing other systems than silver halide photographic systems. However, there are disadvantages in such photographic silver halide light-sensitive elements. For example, the photographic light-sensitive element must be developed in an aqueous developer, after exposure, and the developed light-sensitive element must be subjected'to several processings in order to prevent the thus developedimage from becoming-discolored or faded, and to prevent the colorof the background thereof from blackening. The latter processings are usually called stopping, fixing" and stabilizing" in usual photographic methods. Therefore, it is very desirable to simplify processing, such as developing, fixing and the like in silver halide photography and to provide a stable and permanent image.

For realizing such a desire, many efforts have hitherto been made.

One of them is so-called a monobath developing and fixing process in which the development and fixing are conducted in one process in silver halide photography. See, for example, U.S. Pat. No. 2,875,048; British Pat. No. 954,453; and German Pat. No. 1,163,142.

Another attempt is one in which the wet type processing in silver halide photography are conducted in a dry manner instead of employing the conventional wet system. Such an attempt is disclosed, e.g., in the Specifications of German Pat. No. 1,174,159; British Pat. No. 943,476 and 951,644.

Still another attempt is one in which a silver salt compound other than silver halide is mainly used and is disclosed e.'g., in the specifications of U.S. Pat. No. 3,152,904, Belgian Pat. No. 663,112 and our copending U.S. Pat. application No. 617,498 and 643,828.

The light-sensitive element employed in the present invention is one which belongs to the third class of the aforesaid attempts. That is, the light-sensitive element processed by the process of this invention contains a combination of a light-insensitive and reducible organic silver salt and a slight amount of a light-sensitive silver salt, in particular, a combination of a silver salt of benzotriazole and a slight amount of a silver ha lide.

The inventors have found previously that stable photographic images can be obtained by a dry process after imagewise exposure without the necessity of wet development, wet fixing, etc., by employing a thermally developable light-sensitive element having at least one layer containing at least (a) a light insensitive and reducible organic silver salt, such as a salt of benzotriazole, (b) a slight amount of a material which provides a light-sensitive material, that is, an inorganic halide capable of forming a light-sensitive silver halide by reaction with the light-insensitive and reducible organic silver salt (a) as above, (c) a reducing agent, and (d) an organic acid or a salt thereof. The photographic image thus formed by the thermal development can be stored stably for a long period at normal temperature even under White light without further processing, such as fixing and stabilizing but if the image thus formed by thermal development is stored under conditions of high temperature and high humidity, the development proceeds gradually even though it is very slight and hence the background turns brown gradually. Ac-

developed by heating.

Still other objects advantages advantages of this invention will become apparent from the following detailed description. It is well known that a photographic silver halide light-sensitive element is stabilized, after exposureand development, by processing in an aqueous solution of various inorganic and organic compounds, whereby only the silver halide which has not been developed in the above development is converted into a compound inactive to light. For example, in British Pat. Specification No. 631,184 there are illustrated, as such a stabilizer, an organic compound containing a sulfur atom having double bond, or SH radical, a compound containing a quaternary nitrogen atom, an alkali metal salt of a thiosulfate. and ammonium thiosulfate. Also, in British Pat. Specification No. 867,242, there is disclosed ammonium thiosulfate as the stabilizer. These stabilizers are all used as aqueous solutions.

The feature of the present invention is a stabilization process for stabilizing the image developed after imagewise exposure by heating a thermally developable light-sensitive element containing a light-insensitive and reducible organic salt, such as a salt of benzotriazole, and a slight amount of a light-sensitive silver salt such as silver halide, in which a slight amount of the light-sensitive silver halide remaining in unexposed portions is caused to react with a stabilizer to be converted into a" compound which is stable to light and ineffective as a reducing catalyst for the reducible organic silver salt when the element is exposed to light after the development by heat. The stabilization process of the present invention willbe explained below.

According-to the process of this invention, a thermally developable light-sensitive element disclosed, e.g., in our copending U.S. Pat. application No. 617,498 and 643,828 that is, a thermally developable light-sensitive element having at least one layer containing at least a light-insensitive and reducible organic silver salt, such as a salt of benzotriazole and a slight amount of a light-sensitive silver salt is exposed, developed thermally, and processed for a short time by a solution of the compound shown below to stabilize the light-sensitive elementand to provide permanent images stable to light.

In the practice of the process of this invention, the following three groups of stabilizers have been investigated. That is, the inventors have investigated the stabilization effects or actions of compounds conventionally employed for stabilizing conventional photographic light-sensitive elements wherein lightsensitive silver halide is mainly used as the light-sensitive material as well as other organic compounds capable offorming compounds inactive or insensitive to light by reaction with silver ions.

1. Group 1:

The stabilizing agents belonging to group 1 are organic compounds represented by the following general formula:

group, a tetrazolyl group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridazinyl group, and a triazinyl group.

As the suitable examples of the compounds shown by aforesaid general formula and preferably employed in the process of this invention. there are illustrated 2-mercaptoimidazole, 2-mercaptobenzimidazole, -carboethoxy-2- mercapto-4-methylthiazole, 2-mercaptobenzothiazole, 2-mercaptoxazole, 2-mercaptobenzoxazole, 3-mercapto-4-phenyl- 1,2,4-triazole, 3-mercapto-4, S-dimethyl-l,2,4-triazole, 4- mercapto-6 methyl-1,3,3a, 7-tetrazaindene, 2-methylthio- 4methylthiazole-5-thione, 3-phenyl-2-oxadiazoline-5-thione, l-phenyl-5-mercaptotetrazole, 3-mercaptopyridine, 4-hydroxy-2-mercapto-6methylpyrimidine, Z-mercaptopyt'adine, 3- mercaptopyridazine, 2,4,6,-trimercapto-l ,3,5-triazine and the like.

II. Group 2:

The stabilizing agents belonging to group 2 are substituted or unsubstituted thioureas represented by the following general formula:

Rg Rt wherein R R R R R and R each represents a hydrogen atom, an alkyl group, an aryl group, an allyl group, an aralkyl group, or an acyl group, and Y represents an atomic group necessary for forming substituted or unsubstituted diazolidinethione ring with N-C-N- Examples of the compounds shown by the above formula and particularly investigated by us are thiourea, l, 3- dimethylthiourea, tetramethylthiourea, allylthiourea, phenylthiourea, 2.2'ditolythiourea, 4,4'-ditolylthiourea, benzylthiourea, acetylthiourea, ethylene thiourea, 2-thiohydantoin.

III. Group 3:

The stabilizing agents belonging to group 3 are thiocyanates represented by the general formula:

Z-(SCN),

wherein 2 represents an alkali metal, an alkaline earth metal, ammonium, an alkyl group, an aryl group, an allyl group or an aralkyl group and n is the valence ofgroup Z.

The compounds represented by the above formula and investigated by us are potassium thiocyanate, barium thiocyanate, ammonium thiocyanate, methyl thiocyanate, allyl thiocynate, phenyl thiocyanate. 2,4-dinitro-phenyl thiocyanate, benzyl thiocyanate.

As the results ofour investigation concerning the stabilizing agents belonging to the aforesaid three groups, it was found that the stabilizing agents belonging to group 2 are not suitable for the process of this invention since when the concentration of the stabilizing solution is increased, the images formed by thermal development disappear, and when the concentration thereof is decreased, the quality of the reproduction copies or images is extremely reduced, and the contrast between image area and background area decreases. lt also was found that the stabilizing agents belonging to group 3 are not suitable for the process of this invention either, since when the concentration of the stabilizing solution is increased, the images disappear, and when the concentration thereof is decreased, the images are not stabilized. On the other hand, it has been found that the stabilizing agents belonging to group 1 are very suitable for the process of this invention.

SUMMARY OF THE INVENTION That is, the process of this invention is a stabilization process for stabilizing the image developed, after imagewise exposure, by heating a thermally developable light-sensitive element having at least one layer containing at least (a) a light-insensitive and reducible silver salt such as a silver salt of benzotriazole, (b) an inorganic halide capable of forming a silver halide by reaction with the silver salt (a) or a silver halide, (c) a reducing agent, and (d) an organic acid or a salt thereof, which comprises processing said light-sensitive element by a stabilizing solution containing the stabilizing agent belonging to aforesaid group I to provide permanent images or reproductions.

DETAILED DESCRIPTION OF THE INVENTION The concentration of the stabilizing agent used in the present invention is influenced by the method of processing and the processing time, e.g., the time of immersion of the light-sensitive element in the stabilizing solution, but a suitable concentration of the stabilizing solution is in the range of up to 20% by weight, and preferably of from 0.5% to 5% by weight. Further, as the solvent for the stabilizing agent, a solvent having a high permeability into the light-sensitive layer is effective. The most suitable solvents are such volatile solvents as methanol, ethanol, acetone, toluene and dioxane.

The use of a volatile organic solvent also provides the additional merit that the light-sensitive element stabilized by the process of the present invention can be dried more quickly than in the case of using an aqueous stabilizing solution as in the case of processing conventional photographic silver halide light sensitive elements.

Now, the invention will be practically explained by the following examples.

The thermally developable light-sensitive elements used in examples 1 to 5 were prepared by the following procedure:

To a photographic paper there was applied, per 1 square meter, a uniform dispersion having the following composition:

Polyvinyl Butyral l8 ml. (15% methanol solution) Silver Salt of Benzotriazole l5 ml.

(l5'7r methanol dispersion) Potassium iodide l5 ml.

(l/SO N methanol solution) sensitizing dye 0.36 ml. (0.25% methanol solution] I-Ascorhyl palmitatc 0.12 g. Schacic acid 2.4 g.

EXAMPLE I The thermally developable light-sensitive paper prepared above was exposed, developed by heating, and immersed for 2 seconds in a nonaqueous stabilizing solution having the following composition:

5-Mercapto l -phenyltetrazole Methanol 2.5 g. I00 ml.

The images processed by the stabilizing solution of this invention showed sufficient stability after drying. As a severe test, the sample thus stabilized was allowed to stand exposed in a light place for 12 hours and was then stored for 3 days under severe conditions at a temperature of 50 C. and a relative humidity of But there could not be observed any degradation of the properties of the images such as the reduction in image density and discoloring ofthe background areas.

Also, when the light-sensitive element stabilized by the stabilizing solution ofthis invention was heated again to the thermal development temperature, no development proceeded and the images remained stable without being degraded.

EXAMPLEZ 3-Mercspto-4-phenyll .2,4-triszolc Ethanol 5.0 g. I ml.

EXAMPLE 3 After exposing and developing by heating as in example 1, the thermally developable light-sensitive paper was immersed for one second in a stabilizing solution having the following composition:

2-mercaptobenzimidazole methanol 2.0 g. 100 ml.

THe images processed by the stabilizing solution of this invention also showed sufficient stability after drying. As in example 2 development did not proceed when the stabilized light-sensitive element was heated again to the thermal development temperature.

EXAMPLE 4 The same procedure as in example 1 was repeated using a stabilization solution having the following composition and immersing therein for one second:

Z-Mercaptobenzothiazole M ethanol 2.0 g. 100 ml.

The images processed by the stabilizing solution of this invention showed sufficient stability after drying. When the light-sensitive element thus processed was heated again to the thermal development temperature, no development proceeded.

EXAMPLE 5 The same procedure as in example 1 was repeated using a stabilizing solution having the following composition and immersing the element therein for one second:

2.0 g. I00 ml.

The image thus processed showed sufl'lcient stability after drying and when the stabilized light-sensitive element was heated again to the thermal development temperature, no development proceeded.

What is claimed is:

l. A stabilized, thermally developed light-sensitive element comprising a support having a layer thereon consisting of at least the following components:

a. a silver salt of benzotriazole,

b. at least one member selected from the group consisting of an inorganic halide capable of forming a silver halide by reaction with said silver salt of benzotriazole and a silver halide,

c. a reducing agent, and

d. at least one member selected from the of an or anic acid and a salt thereof, said elemen having been stabilized, afier development,

group consisting 

